Electrochemical device, energy system and solid oxide fuel cell

ABSTRACT

Provided are a low-cost electrochemical device and the like that have both durability and high performance as well as excellent reliability. The electrochemical device includes at least one metal material, and the metal material is made of a Fe—Cr alloy that contains Ti in an amount of more than 0.10 mass % and 1.0 mass % or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the United States national phase of InternationalApplication No. PCT/JP2018/013690 filed Mar. 30, 2018, and claimspriority to Japanese Patent Application No. 2017-073163 filed Mar. 31,2017, the disclosures of which are hereby incorporated by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to an electrochemical device including ametal material, and the like.

BACKGROUND ART

In conventional metal-supported solid oxide fuel cells (SOFCs) in whichmetal is used as materials for forming an interconnector, a separator,and the like, a Fe—Cr based alloy such as Crofer 22 APU whose thermalexpansion coefficient is close to those of an electrode material, anelectrolyte material, and the like for the SOFC is used as thematerials.

PRIOR ART DOCUMENTS Patent Document

Patent Document 1: JP 2008-529244A

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, as shown in the prior art, there is a problem in that, when aconventional metal material such as Crofer 22 APU is used, a Crcomponent volatilizes from the metal material and poisons otherconstituent elements such as an electrode material for a fuel cell, thusmaking it difficult to ensure the durability of the device.

It should be noted that the above-described SOFCs, solid oxideelectrolytic cells (referred to as “SOECs” hereinafter) that producehydrogen through electrolysis of water, oxygen sensors using a solidoxide, and the like have a common basic structure. That is,electrochemical elements including a metal substrate, an electrodelayer, and an electrolyte layer are used in the SOFCs, SOECs, and oxygensensors. The above-described problem is common to the above-describedelectrochemical elements, SOFCs, SOECs, and oxygen sensors.

The present invention was achieved in light of the foregoing problem,and an object of the present invention is to provide a low-costelectrochemical device and the like that have both durability and highperformance as well as excellent reliability.

Means for Solving Problem

A characteristic configuration of an electrochemical device forachieving the object includes at least one metal material, wherein themetal material is made of a Fe—Cr based alloy that contains Ti in anamount of more than 0.10 mass % and 1.0 mass % or less.

Ti is likely to form stable carbides through a reaction with carbon in asteel material. With the above-mentioned characteristic configuration,the electrochemical device includes at least one metal material, and themetal material is made of a Fe—Cr based alloy that contains Ti in anamount of more than 0.10 mass % and 1.0 mass % or less. Therefore, theeffect of improving oxidation resistance and high-temperature strengthof the Fe—Cr alloy is obtained, thus making it possible to suppressvolatilization of Cr from the metal material even during long periods ofuse at high temperatures, and making it possible to realize anelectrochemical device that has excellent durability.

It should be noted that the content of Ti is preferably 0.15 mass % ormore, and more preferably 0.20 mass % or more. The reason for this isthat the effect of improving oxidation resistance and high-temperaturestrength of the Fe—Cr alloy due to the addition of Ti can be madegreater. Moreover, the content of Ti is preferably 0.90 mass % or less,and more preferably 0.80 mass % or less. The reason for this is that anincrease in the cost of the Fe—Cr based alloy due to the addition of Tican be suppressed.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, the metal material contains Cu in anamount of 0.10 mass % or more and 1.0 mass % or less.

Cu has an effect of reducing contact resistance (electric resistance).With the above-mentioned characteristic configuration, the metalmaterial contains Cu in an amount of 0.10 mass % or more and 1.0 mass %or less, thus making it possible to suppress the electric resistancevalue of the electrochemical device to a low level, and making itpossible to realize a high-performance electrochemical device.

It should be noted that the content of Cu is preferably 0.20 mass % ormore, and more preferably 0.30 mass % or more. The reason for this isthat the effect of reducing contact resistance due to the addition of Cuto the Fe—Cr based alloy can be made greater. Moreover, the content ofCu is preferably 0.90 mass % or less, and more preferably 0.70 mass % orless. The reason for this is that an increase in the cost due to theaddition of Cu to the Fe—Cr based alloy can be suppressed.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, the metal material contains Cr in anamount of 18 mass % or more and 25 mass % or less.

The above-mentioned characteristic configuration makes it possible tobring the thermal expansion coefficient of the Fe—Cr based alloy closeto the thermal expansion coefficients of a zirconia-based material and aceria-based material contained in the materials for forming an electrodelayer and an electrolyte layer of a SOFC, for example, thus making itpossible to suppress breakage and separation of the electrode layer andthe electrolyte layer even in a case where the electrochemical device isused at high temperatures or a heat cycle is performed, and making itpossible to realize a highly reliable electrochemical device.

It should be noted that the content of Cr is more preferably 20 mass %or more. The reason for this is that the thermal expansion coefficientof the Fe—Cr based alloy can be brought closer to the thermal expansioncoefficients of the zirconia-based material and the ceria-basedmaterial. Moreover, the upper limit of the content of Cr is morepreferably 23 mass % or less. The reason for this is that an increase inthe cost of the Fe—Cr based alloy can be suppressed.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, the metal material contains no rareearth elements.

The above-mentioned characteristic configuration is preferable because areduction in the cost of the Fe—Cr based alloy material can be realizedby refraining from using expensive atoms, so that a low-costelectrochemical device can be realized.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, the metal material is made of amagnetic substance.

With the above-mentioned characteristic configuration, the material canbe fixed using a magnet when the metal material undergoes processing oris joined to another constituent component, for example, thus making itpossible to realize an electrochemical device using a low-costtechnique.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, a portion or all of a surface of themetal material is covered with a metal oxide thin layer.

With the above-mentioned characteristic configuration, the metal oxidecoating can suppress dispersion of the components such as Cr of themetal material, thus making it possible to suppress a decrease inperformance of the electrochemical device.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, the metal material is used for aseparator.

Here, the separator refers to a component for separating passages suchthat a plurality of types of reaction gas used in the electrochemicaldevice are not mixed with each other. With the above-mentionedcharacteristic configuration, excellent reliability is imparted to anelectrochemical device by bringing the thermal expansion coefficient ofthe separator close to those of the electrode material and the likewhile suppressing the amount of volatilized Cr and ensuring durability,and, in addition, the performance of the electrochemical device isincreased by suppressing the electric resistance to a low level.Furthermore, refraining from using expensive atoms makes it possible torealize a low-cost electrochemical device.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, the metal material is used for amanifold.

Here, the manifold refers to a component for supplying reaction gas toan element (e.g., electrochemical element) in which an electrochemicalreaction occurs. With the above-mentioned characteristic configuration,excellent reliability is imparted to an electrochemical device bybringing the thermal expansion coefficient of the manifold close tothose of the electrode material and the like while suppressing theamount of volatilized Cr and ensuring durability, and, in addition, theperformance of the electrochemical device is increased by suppressingthe electric resistance to a low level. Furthermore, refraining fromusing expensive atoms makes it possible to realize a low-costelectrochemical device.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, the metal material is used for aninterconnector.

Here, the interconnector refers to a component for connecting, to eachother, a plurality of elements (e.g., electrochemical elements) in whichan electrochemical reaction occurs. With the above-mentionedcharacteristic configuration, excellent reliability is imparted to anelectrochemical device by bringing the thermal expansion coefficient ofthe interconnector close to those of the electrode material and the likewhile suppressing the amount of volatilized Cr and ensuring durability,and, in addition, the performance of the electrochemical device isincreased by suppressing the electric resistance to a low level.Furthermore, refraining from using expensive atoms makes it possible torealize a low-cost electrochemical device.

In another characteristic configuration of the electrochemical deviceaccording to the present invention, the metal material is used for acurrent collector.

Here, the current collector refers to a component that is provided to bein contact with an element (e.g., electrochemical element) in which anelectrochemical reaction occurs and that extracts electricity from theelement. With the above-mentioned characteristic configuration,excellent reliability is imparted to an electrochemical device bybringing the thermal expansion coefficient of the current collectorclose to those of the electrode material and the like while suppressingthe amount of volatilized Cr and ensuring durability, and, in addition,the performance of the electrochemical device is increased bysuppressing the electric resistance to a low level. Furthermore,refraining from using expensive atoms makes it possible to realize alow-cost electrochemical device.

Another characteristic configuration of the electrochemical deviceaccording to the present invention includes at least an electrochemicalelement and a reformer, and includes a fuel supply unit which suppliesfuel gas containing a reducible component to the electrochemicalelement.

The above-mentioned characteristic configuration includes at least theelectrochemical element and the reformer, and the fuel supply unit whichsupplies the fuel gas containing a reducible component to theelectrochemical element, thus making it possible to use an existing rawfuel supply infrastructure such as city gas, and making it possible torealize an electrochemical device that has excellent durability,reliability, and performance that can obtain electrical output from theelectrochemical element or a module thereof. Also, it is easier toconstruct a system that recycles unused fuel gas discharged from theelectrochemical element or the module thereof, thus making it possibleto realize a highly efficient electrochemical device.

Another characteristic configuration of the electrochemical deviceaccording to the present invention includes at least the above-describedelectrochemical element and an inverter that extracts electrical powerfrom the electrochemical element.

The above-mentioned characteristic configuration is preferable becauseit makes it possible to boost, using an inverter, electrical outputobtained from the electrochemical element or a module thereof or toconvert a direct current into an alternating current, and thus makes iteasy to use the electrical output obtained from the electrochemicaldevice.

A characteristic configuration of an energy system according to thepresent invention includes the above-described electrochemical device,and a waste heat management unit that reuses heat discharged from theelectrochemical device.

The above-mentioned characteristic configuration includes theabove-described electrochemical device and the waste heat managementunit that reuses heat discharged from the electrochemical device, thusmaking it possible to realize an energy system that has excellentdurability, reliability, and performance as well as excellent energyefficiency. It should be noted that it is also possible to realize ahybrid system that has excellent energy efficiency by combination with apower generation system that generates power with use of combustion heatfrom unused fuel gas discharged from the electrochemical device.

A characteristic configuration of a solid oxide fuel cell according tothe present invention includes the above-described electrochemicaldevice, wherein a power generation reaction is caused therein.

With the above-mentioned characteristic configuration, it is possible tosuppress deterioration of an electrochemical element and maintain theperformance of the fuel cell for a long period of time while high powergeneration performance is exhibited. It should be noted that a solidoxide fuel cell that can be operated in a temperature range of 650° C.or higher during the rated operation is more preferable because a fuelcell system that uses hydrocarbon-based raw fuel such as city gas can beconstructed such that waste heat discharged from a fuel cell can be usedin place of heat required to convert raw fuel to hydrogen, and the powergeneration efficiency of the fuel cell system can thus be improved. Asolid oxide fuel cell that can be operated in a temperature range of900° C. or lower during the rated operation is preferable because theeffect of suppressing volatilization of Cr from the electrochemicaldevice can be improved, and a solid oxide fuel cell that can be operatedin a temperature range of 850° C. or lower during the rated operation ismore preferable because the effect of suppressing volatilization of Crcan be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a configuration of anelectrochemical element.

FIG. 2 is a schematic diagram showing configurations of electrochemicalelements and an electrochemical module.

FIG. 3 is a schematic diagram showing configurations of anelectrochemical device and an energy system.

FIG. 4 is a schematic diagram showing a configuration of anelectrochemical module.

BEST MODES FOR CARRYING OUT THE INVENTION First Embodiment

Hereinafter, an electrochemical element E and a solid oxide fuel cell(SOFC) according to this embodiment will be described with reference toFIG. 1. The electrochemical element E is used as a constituent elementof a solid oxide fuel cell that receives a supply of air and fuel gascontaining hydrogen and generates power, for example. It should be notedthat when the positional relationship between layers and the like aredescribed in the description below, a counter electrode layer 6 side maybe referred to as “upper portion” or “upper side”, and an electrodelayer 2 side may be referred to as “lower portion” or “lower side”, withrespect to an electrolyte layer 4, for example. In addition, in a metalsubstrate 1, a surface on/over which the electrode layer 2 is formed maybe referred to as “front side”, and a surface on an opposite side may bereferred to as “back side”.

Electrochemical Element

As shown in FIG. 1, the electrochemical element E includes a metalsubstrate 1 (metal support), an electrode layer 2 formed on/over themetal substrate 1, an intermediate layer 3 formed on/over the electrodelayer 2, and an electrolyte layer 4 formed on/over the intermediatelayer 3. The electrochemical element E further includes a reactionpreventing layer 5 formed on/over the electrolyte layer 4, and a counterelectrode layer 6 formed on/over the reaction preventing layer 5.Specifically, the counter electrode layer 6 is formed above theelectrolyte layer 4, and the reaction preventing layer 5 is formedbetween the electrolyte layer 4 and the counter electrode layer 6. Theelectrode layer 2 is porous, and the electrolyte layer 4 is dense.

Metal Substrate

The metal substrate 1 plays a role as a support that supports theelectrode layer 2, the intermediate layer 3, the electrolyte layer 4,and the like and maintains the strength of the electrochemical elementE. A material that has excellent electron conductivity, thermalresistance, oxidation resistance, and corrosion resistance is used asthe material for forming the metal substrate 1. Examples thereof includeferrite-based stainless steel, austenite-based stainless steel, andnickel alloys. In particular, alloys containing chromium are favorablyused. It should be noted that although a plate-shaped metal substrate 1is used as the metal support in this embodiment, a metal support havinganother shape such as a box shape or cylindrical shape can also be used.

It should be noted that the metal substrate 1 need only have a strengthsufficient for serving as the support for forming the electrochemicalelement, and can have a thickness of approximately 0.1 mm to 2 mm,preferably approximately 0.1 mm to 1 mm, and more preferablyapproximately 0.1 mm to 0.5 mm, for example.

The material for forming the metal substrate 1 may be any one of a Fe—Crbased alloy that contains Ti in an amount of 0.15 mass % or more and 1.0mass % or less, a Fe—Cr based alloy that contains Zr in an amount of0.15 mass % or more and 1.0 mass % or less, and a Fe—Cr based alloy thatcontains Ti and Zr, a total content of Ti and Zr being 0.15 mass % ormore and 1.0 mass % or less. In addition, the metal substrate 1 maycontain Cu in an amount of 0.10 mass % or more and 1.0 mass % or less,and may contain Cr in an amount of 18 mass % or more and 25 mass % orless.

The metal substrate 1 is provided with a plurality of through holes 1 athat penetrate the surface on the front side and the surface on the backside. It should be noted that the through holes 1 a can be provided inthe metal substrate 1 through mechanical, chemical, or optical piercingprocessing, for example. The through holes 1 a have a function oftransmitting gas from the surface on the back side of the metalsubstrate 1 to the surface on the front side thereof. Porous metal canalso be used to impart gas permeability to the metal substrate 1. Ametal sintered body, a metal foam, or the like can also be used as themetal substrate 1, for example.

A metal oxide thin layer 1 b serving as a diffusion suppressing layer isprovided on/over the surfaces of the metal substrate 1. That is, thediffusion suppressing layer is formed between the metal substrate 1 andthe electrode layer 2, which will be described later. The metal oxidethin layer 1 b is provided not only on/over the surface of the metalsubstrate 1 exposed to the outside but also the surface (interface) thatis in contact with the electrode layer 2 and the inner surfaces of thethrough holes 1 a. Element interdiffusion that occurs between the metalsubstrate 1 and the electrode layer 2 can be suppressed due to thismetal oxide thin layer 1 b. For example, when ferrite-based stainlesssteel containing chromium is used in the metal substrate 1, the metaloxide thin layer 1 b is mainly made of a chromium oxide. The metal oxidethin layer 1 b containing the chromium oxide as the main componentsuppresses diffusion of chromium atoms and the like of the metalsubstrate 1 to the electrode layer 2 and the electrolyte layer 4. Themetal oxide thin layer 1 b need only have such a thickness that allowsboth high diffusion preventing performance and low electric resistanceto be achieved. For example, it is preferable that the thickness is onthe order of submicrons to several microns.

The metal oxide thin layer 1 b can be formed using various techniques,but it is favorable to use a technique of oxidizing the surface of themetal substrate 1 to obtain a metal oxide. Also, the metal oxide thinlayer 1 b may be formed on/over the surface of the metal substrate 1 byusing a PVD technique such as a sputtering technique or PLD technique, aCVD technique, or a spray coating technique (a technique such as thermalspraying technique, an aerosol deposition technique, an aerosol gasdeposition technique, a powder jet deposition technique, a particle jetdeposition technique, or a cold spraying technique), or may be formed byplating and oxidation treatment. Furthermore, the metal oxide thin layer1 b may also contain a spinel phase that has high electron conductivity,or the like.

When a ferrite-based stainless steel material is used to form the metalsubstrate 1, its thermal expansion coefficient is close to that of YSZ(yttria-stabilized zirconia), GDC (gadolinium-doped ceria; also calledCGO), or the like, which is used as the material for forming theelectrode layer 2 and the electrolyte layer 4. Accordingly, even if lowand high temperature cycling is repeated, the electrochemical element Eis not likely to be damaged. Therefore, this is preferable due to beingable to realize an electrochemical element E that has excellentlong-term durability.

Electrode Layer

As shown in FIG. 1, the electrode layer 2 can be provided as a thinlayer in a region that is larger than the region provided with thethrough holes 1 a, on the front surface of the metal substrate 1. Whenit is provided as a thin layer, the thickness can be set toapproximately 1 μm to 100 μm, and preferably 5 μm to 50 μm, for example.This thickness makes it possible to ensure sufficient electrodeperformance while also achieving cost reduction by reducing the usedamount of expensive electrode layer material. The region provided withthe through holes 1 a is entirely covered with the electrode layer 2.That is, the through holes 1 a are formed inside the region of the metalsubstrate 1 in which the electrode layer 2 is formed. In other words,all the through holes 1 a are provided facing the electrode layer 2.

A composite material such as NiO-GDC, Ni-GDC, NiO—YSZ, Ni—YSZ, CuO—CeO₂,or Cu—CeO₂ can be used as the material for forming the electrode layer2, for example. In these examples, GDC, YSZ, and CeO₂ can be called theaggregate of the composite material. It should be noted that it ispreferable to form the electrode layer 2 using low-temperature heating(not performing heating treatment in a high temperature range of higherthan 1100° C., but rather performing a wet process using heatingtreatment in a low temperature range, for example), a spray coatingtechnique (a technique such as a thermal spraying technique, an aerosoldeposition technique, an aerosol gas deposition technique, a powder jetdeposition technique, a particle jet deposition technique, or a coldspraying technique), a PVD technique (e.g., a sputtering technique or apulse laser deposition technique), a CVD technique, or the like. Due tothese processes that can be used in a low temperature range, a favorableelectrode layer 2 is obtained without using heating in a hightemperature range of higher than 1100° C., for example. Therefore, thisis preferable due to being able to prevent damage to the metal substrate1, suppress element interdiffusion between the metal substrate 1 and theelectrode layer 2, and realize an electrochemical element that hasexcellent durability. Furthermore, using low-temperature heating makesit possible to facilitate handling of raw materials and is thus morepreferable.

The inside and the surface of the electrode layer 2 are provided with aplurality of pores in order to impart gas permeability to the electrodelayer 2.

That is, the electrode layer 2 is formed as a porous layer. Theelectrode layer 2 is formed to have a denseness of 30% or more and lessthan 80%, for example. Regarding the size of the pores, a size suitablefor smooth progress of an electrochemical reaction can be selected asappropriate. It should be noted that the “denseness” is a ratio of thematerial of the layer to the space and can be represented by a formula“1—porosity”, and is equivalent to relative density.

Intermediate Layer

As shown in FIG. 1, the intermediate layer 3 can be formed as a thinlayer on/over the electrode layer 2 so as to cover the electrode layer2. When it is formed as a thin layer, the thickness can be set toapproximately 1 μm to 100 μm, preferably approximately 2 μm to 50 μm,and more preferably approximately 4 μm to 25 μm, for example. Thisthickness makes it possible to ensure sufficient performance while alsoachieving cost reduction by reducing the used amount of expensiveintermediate layer material. YSZ (yttria-stabilized zirconia), SSZ(scandium-stabilized zirconia), GDC (gadolinium-doped ceria), YDC(yttrium-doped ceria), SDC (samarium-doped ceria), or the like can beused as the material for forming the intermediate layer 3. Inparticular, ceria-based ceramics are favorably used.

It is preferable to form the intermediate layer 3 using low-temperatureheating (not performing heating treatment in a high temperature range ofhigher than 1100° C., but rather performing a wet process using heatingtreatment in a low temperature range, for example), a spray coatingtechnique (a technique such as a thermal spraying technique, an aerosoldeposition technique, an aerosol gas deposition technique, a powder jetdeposition technique, a particle jet deposition technique, or a coldspraying technique), a PVD technique (e.g., a sputtering technique or apulse laser deposition technique), a CVD technique, or the like. Due tothese film formation processes that can be used in a low temperaturerange, an intermediate layer 3 is obtained without using heating in ahigh temperature range of higher than 1100° C., for example. Therefore,it is possible to prevent damage to the metal substrate 1, suppresselement interdiffusion between the metal substrate 1 and the electrodelayer 2, and realize an electrochemical element E that has excellentdurability. Furthermore, using low-temperature heating makes it possibleto facilitate handling of raw materials and is thus more preferable.

It is preferable that the intermediate layer 3 has oxygen ion (oxideion) conductivity. It is more preferable that the intermediate layer 3has both oxygen ion (oxide ion) conductivity and electron conductivity,namely mixed conductivity. The intermediate layer 3 that has theseproperties is suitable for application to the electrochemical element E.

It is preferable that the intermediate layer 3 does not includecatalytic metal components such as Ni and Cu. The reason for this isthat the inclusion of the catalytic metal components such as Ni and Cumakes it less likely to obtain a desired intermediate layer 3.

Electrolyte Layer

As shown in FIG. 1, the electrolyte layer 4 is formed as a thin layeron/over the intermediate layer 3 so as to cover the electrode layer 2and the intermediate layer 3. Specifically, as shown in FIG. 1, theelectrolyte layer 4 is provided on/over both the intermediate layer 3and the metal substrate 1 (spanning the intermediate layer 3 and themetal substrate 1). Configuring the electrolyte layer 4 in this mannerand joining the electrolyte layer 4 to the metal substrate 1 make itpossible to allow the electrochemical element to have excellenttoughness as a whole.

Also, as shown in FIG. 1, the electrolyte layer 4 is provided in aregion that is larger than the region provided with the through holes 1a, on/over the front surface of the metal substrate 1. That is, thethrough holes 1 a are formed inside the region of the metal substrate 1in which the electrolyte layer 4 is formed.

The leakage of gas from the electrode layer 2 and the intermediate layer3 can be suppressed in the vicinity of the electrolyte layer 4. Adescription of this will be given. When the electrochemical element E isused as a constituent element of a SOFC, gas is supplied from the backside of the metal substrate 1 through the through holes 1 a to theelectrode layer 2 during the operation of the SOFC. In a region wherethe electrolyte layer 4 is in contact with the metal substrate 1,leakage of gas can be suppressed without providing another componentsuch as a gasket. It should be noted that although the entire vicinityof the electrode layer 2 is covered with the electrolyte layer 4 in thisembodiment, a configuration in which the electrolyte layer 4 is providedon/over the electrode layer 2 and the intermediate layer 3 and a gasketor the like is provided in its vicinity may also be adopted.

YSZ (yttria-stabilized zirconia), SSZ (scandium-stabilized zirconia),GDC (gadolinium-doped ceria), YDC (yttrium-doped ceria), SDC(samarium-doped ceria), LSGM (strontium- and magnesium-doped lanthanumgallate), or the like can be used as the material for forming theelectrolyte layer 4. In particular, zirconia-based ceramics arefavorably used. Using zirconia-based ceramics for the electrolyte layer4 makes it possible to increase the operation temperature of the SOFC inwhich the electrochemical element E is used compared with the case whereceria-based ceramics are used. For example, when the electrochemicalelement E is used in the SOFC, by adopting a system configuration inwhich a material such as YSZ that can exhibit high electrolyteperformance even in a high temperature range of approximately 650° C. orhigher is used as the material for forming the electrolyte layer 4, ahydrocarbon-based raw fuel material such as city gas or LPG is used asthe raw fuel for the system, and the raw fuel material is reformed intoanode gas of the SOFC through steam reforming or the like, it is thuspossible to construct a high-efficiency SOFC system in which heatgenerated in a cell stack of the SOFC is used to reform raw fuel gas.

It is preferable to form the electrolyte layer 4 using low-temperatureheating (not performing heating treatment in a high temperature range ofhigher than 1100° C., but rather performing a wet process using heatingtreatment in a low temperature range, for example), a spray coatingtechnique (a technique such as a thermal spraying technique, an aerosoldeposition technique, an aerosol gas deposition technique, a powder jetdeposition technique, a particle jet deposition technique, or a coldspraying technique), a PDV technique (e.g., a sputtering technique or apulse laser deposition technique), a CVD technique, or the like. Due tothese film formation processes that can be used in a low temperaturerange, an electrolyte layer 4 that is dense and has high gas-tightnessand gas barrier properties is obtained without using heating in a hightemperature range of higher than 1100° C., for example. Therefore, it ispossible to prevent damage to the metal substrate 1, suppress elementinterdiffusion between the metal substrate 1 and the electrode layer 2,and realize an electrochemical element E that has excellent performanceand durability. In particular, using low-temperature heating, a spraycoating technique, or the like makes it possible to realize a low-costelement and is thus preferable. Furthermore, using a spray coatingtechnique makes it easy to obtain, in a low temperature range, anelectrolyte layer that is dense and has high gas-tightness and gasbarrier properties, and is thus more preferable.

The electrolyte layer 4 is given a dense configuration in order to blockgas leakage of anode gas and cathode gas and exhibit high ionconductivity. The electrolyte layer 4 preferably has a denseness of 90%or more, more preferably 95% or more, and even more preferably 98% ormore. When the electrolyte layer 4 is formed as a uniform layer, thedenseness is preferably 95% or more, and more preferably 98% or more.When the electrolyte layer 4 has a multilayer configuration, at least aportion thereof preferably includes a layer (dense electrolyte layer)having a denseness of 98% or more, and more preferably a layer (denseelectrolyte layer) having a denseness of 99% or more. The reason forthis is that an electrolyte layer that is dense and has highgas-tightness and gas barrier properties can be easily formed due tosuch a dense electrolyte layer being included as a portion of theelectrolyte layer even when the electrolyte layer has a multilayerconfiguration.

Reaction Preventing Layer

The reaction preventing layer 5 can be formed as a thin layer on/overthe electrolyte layer 4. When it is formed as a thin layer, thethickness can be set to approximately 1 μm to 100 μm, preferablyapproximately 2 μm to 50 μm, and more preferably approximately 4 μm to25 μm, for example. This thickness makes it possible to ensuresufficient performance while also achieving cost reduction by reducingthe used amount of expensive reaction preventing layer material. Thematerial for forming the reaction preventing layer 5 need only becapable of preventing reactions between the component of the electrolytelayer 4 and the component of the counter electrode layer 6. For example,a ceria-based material or the like is used. Introducing the reactionpreventing layer 5 between the electrolyte layer 4 and the counterelectrode layer 6 effectively suppresses reactions between the materialconstituting the counter electrode layer 6 and the material constitutingthe electrolyte layer 4 and makes it possible to improve long-termstability in the performance of the electrochemical element E. Formingthe reaction preventing layer 5 using, as appropriate, a method throughwhich the reaction preventing layer 5 can be formed at a treatmenttemperature of 1100° C. or lower makes it possible to suppress damage tothe metal substrate 1, suppress element interdiffusion between the metalsubstrate 1 and the electrode layer 2, and realize an electrochemicalelement E that has excellent performance and durability, and is thuspreferable. For example, the reaction preventing layer 5 can be formedusing, as appropriate, low-temperature heating, a spray coatingtechnique (a technique such as a thermal spraying technique, an aerosoldeposition technique, an aerosol gas deposition technique, a powder jetdeposition technique, a particle jet deposition technique, or a coldspraying technique), a PVD technique (e.g., a sputtering technique or apulse laser deposition technique), a CVD technique, or the like. Inparticular, using low-temperature heating, a spray coating technique, orthe like makes it possible to realize a low-cost element and is thuspreferable. Furthermore, using low-temperature heating makes it possibleto facilitate handling of raw materials and is thus more preferable.

Counter Electrode Layer

The counter electrode layer 6 can be formed as a thin layer on/over theelectrolyte layer 4 or the reaction preventing layer 5. When it isformed as a thin layer, the thickness can be set to approximately 1 μmto 100 μm, and preferably approximately 5 μm to 50 μm, for example. Thisthickness makes it possible to ensure sufficient electrode performancewhile also achieving cost reduction by reducing the used amount ofexpensive counter electrode layer material. A complex oxide such as LSCFor LSM, or a ceria-based oxide, or a mixture thereof can be used as thematerial for forming the counter electrode layer 6, for example. Inparticular, it is preferable that the counter electrode layer 6 includesa perovskite oxide containing two or more atoms selected from the groupconsisting of La, Sr, Sm, Mn, Co, and Fe. The counter electrode layer 6constituted by the above-mentioned material functions as a cathode.

It should be noted that forming the counter electrode layer 6 using, asappropriate, a method through which the counter electrode layer 6 can beformed at a treatment temperature of 1100° C. or lower makes it possibleto suppress damage to the metal substrate 1, suppress elementinterdiffusion between the metal substrate 1 and the electrode layer 2,and realize an electrochemical element E that has excellent performanceand durability, and is thus preferable. For example, the counterelectrode layer 6 can be formed using, as appropriate, low-temperatureheating, a spray coating technique (a technique such as a thermalspraying technique, an aerosol deposition technique, an aerosol gasdeposition technique, a powder jet deposition technique, a particle jetdeposition technique, or a cold spraying technique), a PDV technique(e.g., a sputtering technique or a pulse laser deposition technique), aCVD technique, or the like. In particular, using low-temperatureheating, a spray coating technique, or the like makes it possible torealize a low-cost element and is thus preferable. Furthermore, usinglow-temperature heating makes it possible to facilitate handling of rawmaterials and is thus more preferable.

Solid Oxide Fuel Cell

The electrochemical element E configured as described above can be usedas a power generating cell for a solid oxide fuel cell. For example,fuel gas containing hydrogen is supplied from the back surface of themetal substrate 1 through the through holes 1 a to the electrode layer2, air is supplied to the counter electrode layer 6 serving as a counterelectrode of the electrode layer 2, and the operation is performed at atemperature of 500° C. or higher and 900° C. or lower, for example.Accordingly, the oxygen O₂ included in air reacts with electrons e⁻ inthe counter electrode layer 6, thus producing oxygen ions O²⁻. Theoxygen ions O²⁻ move through the electrolyte layer 4 to the electrodelayer 2. In the electrode layer 2, the hydrogen H₂ included in thesupplied fuel gas reacts with the oxygen ions O²⁻, thus producing waterH₂O and electrons e⁻. With these reactions, electromotive force isgenerated between the electrode layer 2 and the counter electrode layer6. In this case, the electrode layer 2 functions as a fuel electrode(anode) of the SOFC, and the counter electrode layer 6 functions as anair electrode (cathode).

An electrochemical element E, an electrochemical module M, anelectrochemical device Y, and an energy system Z according to thisembodiment will be described with reference to FIGS. 2 and 3.

As shown in FIG. 2, in the electrochemical element E according to thisembodiment, a U-shaped component 7 is attached to the back surface ofthe metal substrate 1, and the metal substrate 1 and the U-shapedcomponent 7 form a tubular support.

The electrochemical module M is configured by stacking/assembling aplurality of electrochemical elements E with current collectors 26 beingsandwiched therebetween. Each of the current collectors 26 is joined tothe counter electrode layer 6 of the electrochemical element E and theU-shaped component 7, and electrically connects them.

The electrochemical module M includes a gas manifold 17, the currentcollectors 26, a terminal component, and a current extracting unit. Oneopen end of each tubular support in the stack/assembly of the pluralityof electrochemical elements E is connected to the gas manifold 17, andgas is supplied from the gas manifold 17 to the electrochemical elementsE. The supplied gas flows inside the tubular supports, and is suppliedto the electrode layers 2 through the through holes 1 a of the metalsubstrates 1.

FIG. 3 shows an overview of the energy system Z and the electrochemicaldevice Y.

The energy system Z includes the electrochemical device Y, and a heatexchanger 53 serving as a waste heat management unit that reuses heatdischarged from the electrochemical device Y.

The electrochemical device Y includes the electrochemical module M, anda fuel supply unit that includes a desulfurizer 31, and a reformer 34and supplies fuel gas containing a reducible component to theelectrochemical module M, and the electrochemical device Y includes aninverter 38 that extracts electrical power from the electrochemicalmodule M.

Specifically, the electrochemical device Y includes the desulfurizer 31,a reformed water tank (water tank for reforming process) 32, a vaporizer33, the reformer 34, a blower 35, a combustion unit 36, the inverter 38,a control unit 39, a storage container 40, and the electrochemicalmodule M.

The desulfurizer 31 removes sulfur compound components contained in ahydrocarbon-based raw fuel such as city gas (i.e., performsdesulfurization). When a sulfur compound is contained in the raw fuel,the inclusion of the desulfurizer 31 makes it possible to suppress theinfluence that the sulfur compound has on the reformer 34 or theelectrochemical elements E. The vaporizer 33 produces water vapor fromreformed water supplied from the reformed water tank 32. The reformer 34uses the water vapor produced by the vaporizer 33 to perform steamreforming of the raw fuel desulfurized by the desulfurizer 31, thusproducing reformed gas containing hydrogen.

The electrochemical module M generates electricity by causing anelectrochemical reaction to occur with use of the reformed gas suppliedfrom the reformer 34 and air supplied from the blower 35. The combustionunit 36 mixes the reaction exhaust gas discharged from theelectrochemical module M with air, and burns combustible components inthe reaction exhaust gas.

The electrochemical module M includes a plurality of electrochemicalelements E and the gas manifold 17. The electrochemical elements E arearranged side-by-side and electrically connected to each other, and oneend portion (lower end portion) of each of the electrochemical elementsE is fixed to the gas manifold 17. The electrochemical elements Egenerate electricity by causing an electrochemical reaction to occurbetween the reformed gas supplied via the gas manifold 17 and airsupplied from the blower 35. That is, in this embodiment, the gasmanifold 17 functions as a manifold for supplying reaction gas to theelectrochemical elements E. The U-shaped component 7 functions as aseparator for separating passages such that the reformed gas and air arenot mixed with each other.

The inverter 38 adjusts the electrical power output from theelectrochemical module M to obtain the same voltage and frequency aselectrical power received from a commercial system (not shown). Thecontrol unit 39 controls the operation of the electrochemical device Yand the energy system Z.

The vaporizer 33, the reformer 34, the electrochemical module M, and thecombustion unit 36 are stored in the storage container 40. The reformer34 performs reformation processing on the raw fuel with use ofcombustion heat produced by the combustion of reaction exhaust gas inthe combustion unit 36.

The raw fuel is supplied to the desulfurizer 31 via a raw fuel supplypassage 42, due to operation of a booster pump 41. The reformed water inthe reformed water tank 32 is supplied to the vaporizer 33 via areformed water supply passage 44, due to operation of a reformed waterpump 43. The raw fuel supply passage 42 merges with the reformed watersupply passage 44 at a location on the downstream side of thedesulfurizer 31, and the reformed water and the raw fuel, which havebeen merged outside of the storage container 40, are supplied to thevaporizer 33 provided in the storage container 40.

The reformed water is vaporized by the vaporizer 33 to produce watervapor. The raw fuel, which contains the water vapor produced by thevaporizer 33, is supplied to the reformer 34 via a vapor-containing rawfuel supply passage 45. In the reformer 34, the raw fuel is subjected tosteam reforming, thus producing reformed gas that includes hydrogen gasas a main component (first gas including a reducible component). Thereformed gas produced in the reformer 34 is supplied to the gas manifold17 of the electrochemical module M via a reformed gas supply passage 46.

The reformed gas supplied to the gas manifold 17 is distributed amongthe electrochemical elements E, and is supplied to the electrochemicalelements E from the lower ends, which are the connection portions wherethe electrochemical elements E and the gas manifold 17 are connected toeach other. Mainly the hydrogen (reducible component) in the reformedgas is used in the electrochemical reaction in the electrochemicalelements E. The reaction exhaust gas, which contains remaining hydrogengas not used in the reaction, is discharged from the upper ends of theelectrochemical elements E to the combustion unit 36.

The reaction exhaust gas is burned in the combustion unit 36, andcombustion exhaust gas is discharged from a combustion exhaust gasoutlet 50 to the outside of the storage container 40. A combustioncatalyst unit 51 (e.g., a platinum-based catalyst) is provided in thecombustion exhaust gas outlet 50, and reducible components such ascarbon monoxide and hydrogen contained in the combustion exhaust gas areremoved by combustion. The combustion exhaust gas discharged from thecombustion exhaust gas outlet 50 is sent to the heat exchanger 53 via acombustion exhaust gas discharge passage 52.

The heat exchanger 53 uses supplied cool water to perform heat exchangeon the combustion exhaust gas produced by combustion in the combustionunit 36, thus producing warm water. In other words, the heat exchanger53 operates as a waste heat management unit that reuses heat dischargedfrom the electrochemical device Y.

It should be noted that instead of the waste heat management unit, it ispossible to provide a reaction exhaust gas using unit that uses thereaction exhaust gas that is discharged from (not burned in) theelectrochemical module M. The reaction exhaust gas contains remaininghydrogen gas that was not used in the reaction in the electrochemicalelements E. In the reaction exhaust gas using unit, the remaininghydrogen gas is used to achieve effective energy utilization by heatutilization through combustion, power generation in a fuel cell, or thelike.

As described above, the electrochemical device Y according to thisembodiment includes the separators (U-shaped components 7), the manifold(gas manifold 17), and the current collectors 26. In this embodiment, atleast one type of the components made of metal (metal materials), namelythe separators (U-shaped components 7), the manifold (gas manifold 17),and the current collectors 26, is made of a Fe—Cr based alloy thatcontains Ti in an amount of more than 0.10 mass % and 1.0 mass % orless. These metal materials may contain Cu in an amount of 0.10 mass %or more and 1.0 mass % or less, and may contain Cr in an amount of 18mass % or more and 25 mass % or less. It is more preferable that themetal materials contain no rare earth elements and are made of amagnetic substance. It is more preferable that a portion or all of thesurface of each metal material is covered with a metal oxide thin layer.

Second Embodiment

FIG. 4 shows another embodiment of the electrochemical module M. Theelectrochemical module M according to this embodiment is configured bystacking the above-described electrochemical elements E with cellconnecting components 71 (interconnector) being sandwiched therebetween.

The cell connecting components 71 are each a plate-shaped component thathas electron conductivity and does not have gas permeability, and theupper surface and the lower surface are respectively provided withgrooves 72 that are orthogonal to each other. The cell connectingcomponents 71 can be formed using a metal such as stainless steel or ametal oxide.

As shown in FIG. 4, when the electrochemical elements E are stacked withthe cell connecting components 71 being sandwiched therebetween, gas canbe supplied to the electrochemical elements E through the grooves 72.Specifically, the grooves 72 on one side are first gas passages 72 a andsupply gas to the front side of one electrochemical element E, that isto say the counter electrode layer 6. The grooves 72 on the other sideare second gas passages 72 b and supply gas from the back side of oneelectrochemical element E, that is, the back side of the metal substrate1, through the through holes 1 a to the electrode layers 2. That is, inthis embodiment, the cell connecting components 71 function asinterconnectors that couple a plurality of electrochemical element E toeach other.

In the case of operating this electrochemical module M as a fuel cell,oxygen is supplied to the first gas passages 72 a, and hydrogen issupplied to the second gas passages 72 b. Accordingly, a fuel cellreaction progresses in the electrochemical elements E, and electromotiveforce and electrical current are generated. The generated electricalpower is extracted to the outside of the electrochemical module M fromthe cell connecting components 71 at the two ends of the stack ofelectrochemical elements E.

It should be noted that although the grooves 72 that are orthogonal toeach other are respectively formed on the front surface and the backsurface of each of the cell connecting components 71 in this embodiment,grooves 72 that are parallel to each other can be respectively formed onthe front surface and the back surface of each of the cell connectingcomponents 71.

The interconnector (cell connecting component 71) according to thisembodiment is made of a Fe—Cr based alloy that contains Ti in an amountof more than 0.10 mass % and 1.0 mass % or less. This metal material maycontain Cu in an amount of 0.10 mass % or more and 1.0 mass % or less,and may contain Cr in an amount of 18 mass % or more and 25 mass % orless. It is more preferable that the metal material contains no rareearth elements and is made of a magnetic substance. It is morepreferable that a portion or all of the surface of metal material iscovered with a metal oxide thin layer.

The electrochemical module M according to this embodiment can be appliedto the above-described electrochemical device Y. In this case, theelectrochemical device Y includes the above-described interconnectors.

Measurement of Amount of Volatilized Cr

In order to confirm a difference in the amount of volatilized Cr due toa difference in the composition between metal materials, the amount ofvolatilized Cr was measured for each metal material shown in Table 1below. It should be noted that the unit for the values in thecompositions shown in Table 1 is “mass %”. The symbol “−” in the cellsindicates “smaller than or equal to the detection limit”. Metal platesamples with a width of 25 mm and a length of 250 to 300 mm were used,and the metal materials of the metal plate samples were exposed to airat 0.5 L/minute (dew point: 20° C.) at a temperature of 750° C. or 850°C. Then, the amount (integrated amount) of Cr volatilized during apredetermined period of time was measured. Table 2 shows the measurementresults. It should be noted that the unit for the amount of volatilizedCr shown in Table 2 is “μg/600 cm²”, and the values obtained throughconversion into values corresponding to the amount of Cr volatilizedfrom a metal surface area of 600 cm² are shown. It should be noted that,before performing the test to measure the amount of volatilized Cr, allof the samples were subjected to two-stage heating pretreatmentperformed at 850° C. and 1000° C. (this treatment corresponds to theformation of the above-described diffusion suppressing layer).

TABLE 1 Work, Ex. Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3 Comp. Ex. 4 Si0.094 0.01 0.1  0.15 0.25 Mn 0.17 0.4 0.1  0.15 0.48 Cu 0.43 0.001 — —0.02 Ni 0.18 0.16 — — 0.13 Cr 20.82 22 17.3  22.2  16.13  Al 0.04 0.001— — — Mo 0.053 0.001 — 1.1 0.03 Nb 0.008 0.001  0.15 0.3 0.01 Ti 0.3250.06 — 0.1 — La — 0.07 — — —

TABLE 2 750° C. 850° C. 850° C. 250 hours 100 hours 1000 hours Work. Ex530 300 8900 Comp. Ex. 1 530 300 11500  Comp. Ex. 2 690 540 (notmeasured) Comp. Ex. 3 620 460 (not measured) Comp. Ex. 4 600 260 (notmeasured)

As shown in Table 2, in the cases of the samples of Comparative Examples2 to 4, the amount of volatilized Cr increased either in the conditionof 750° C. for 250 hours or in the condition of 850° C. for 100 hours.In the case of the sample of Comparative Example 1, the amount ofvolatilized Cr was the same as that in the case of the sample of WorkingExample in the condition of 750° C. for 250 hours and the condition of850° C. for 100 hours, but the amount of volatilized Cr significantlyincreased in the condition of 850° C. for 1000 hours compared withWorking Example. In the case of the sample of Working Example, theobtained values were favorable in all of the conditions. It wasconfirmed from these results that, in the case of Working Example,volatilization of Cr from the metal support can be suppressed even inlong-period high-temperature environments.

Measurement of Resistance Value

In order to confirm a difference in the electric resistance value due toa difference in the composition between metal materials, the electricresistance value of each of the metal materials of Working Example,Comparative Example 1, and Comparative Example 3 shown in Table 1 wasmeasured. It should be noted that the electric resistance values weremeasured as described below. Gold electrodes were attached to a platemade of each metal material, electrical current was applied theretousing a power source, a voltage for the electrical current was measuredbetween the electrodes that were 10 cm away from each other using avoltmeter, and the electric resistance value was determined from thatvalue. Table 3 shows the results.

TABLE 3 0.1 A 0.2 A 0.3 A 0.5 A application application applicationapplication mV mΩ/cm mV mΩ/cm mV mΩ/cm mV mΩ/cm Work. Ex. 0.3 0.3 0.70.3 1.0 0.3 1.6 0.3 Comp. Ex. 1 0.6 0.6 1.2 0.6 1.8 0.6 3.0 0.6 Comp.Ex. 3 0.8 0.8 1.5 0.7 2.2 0.7 3.6 0.7

It is clear from the results shown in Table 3 that the electricresistance value of the metal material of Working Example is smallerthan those of the metal materials of the comparative examples, and ahigh-performance electrochemical device having a small internalresistance can be realized by using the material of Working Example.

Other Embodiments

(1) Although the electrochemical device in which the metal material ofthe present application is used for a separator, manifold,interconnector, or current collector is shown in the above-mentionedembodiments, the application to various components in which metal isused, such as a stack casing component, a piping component, and apassage component, also makes it possible to suppress volatilization ofCr from the metal materials, thus making it possible realize a low-costelectrochemical device that has excellent durability.

(2) Although the electrochemical elements E are used in a solid oxidefuel cell in the above-mentioned embodiments, the electrochemicalelements E can also be used in a solid oxide electrolyte cell, an oxygensensor using a solid oxide, and the like.

(3) Although the present application is applied to a metal-supportedsolid oxide fuel cell in which the metal substrate 1 serves as a supportin the above-described embodiments, the present application can also beapplied to an electrode-supported solid oxide fuel cell in which theelectrode layer 2 or counter electrode layer 6 serves as a support, oran electrolyte-supported solid oxide fuel cell in which the electrolytelayer 4 serves as a support. In such cases, the functions of a supportcan be obtained by forming the electrode layer 2, counter electrodelayer 6, or electrolyte layer 4 to have a required thickness.

(4) In the above-described embodiments, a composite material such asNiO-GDC, Ni-GDC, NiO—YSZ, Ni—YSZ, CuO—CeO₂, or Cu—CeO₂ is used as thematerial for forming the electrode layer 2, and a complex oxide such asLSCF or LSM is used as the material for forming the counter electrodelayer 6. With this configuration, the electrode layer 2 serves as a fuelelectrode (anode) when hydrogen gas is supplied thereto, and the counterelectrode layer 6 serves as an air electrode (cathode) when air issupplied thereto, thus making it possible to use the electrochemicalelement E as a cell for a solid oxide fuel cell. It is also possible tochange this configuration and thus configure an electrochemical elementE such that the electrode layer 2 can be used as an air electrode andthe counter electrode layer 6 can be used as a fuel electrode. That is,a complex oxide such as LSCF or LSM is used as the material for formingthe electrode layer 2, and a composite material such as NiO-GDC, Ni-GDC,NiO—YSZ, Ni—YSZ, CuO—CeO₂, or Cu—CeO₂ is used as the material forforming the counter electrode layer 6. With this configuration, theelectrode layer 2 serves as an air electrode when air is suppliedthereto, and the counter electrode layer 6 serves as a fuel electrodewhen hydrogen gas is supplied thereto, thus making it possible to usethe electrochemical element E as a cell for a solid oxide fuel cell.

It should be noted that the configurations disclosed in theabove-described embodiments can be used in combination withconfigurations disclosed in other embodiments as long as they arecompatible with each other. The embodiments disclosed in thisspecification are illustrative, and embodiments of the present inventionare not limited thereto and can be modified as appropriate withoutdeparting from the object of the present invention.

INDUSTRIAL APPLICABILITY

The present invention can be applied to an electrochemical element and acell for a solid oxide fuel cell.

LIST OF REFERENCE NUMERALS

-   -   1: Metal substrate    -   1 a: Through hole    -   2: Electrode layer    -   3: Intermediate layer    -   4: Electrolyte layer    -   4: Upper surface of electrolyte layer    -   5: Reaction preventing layer    -   6: Counter electrode layer    -   7: U-shaped component (separator)    -   17: Gas manifold (manifold)    -   26: current collector    -   71: Cell connecting component (interconnector)    -   E: Electrochemical element    -   M: Electrochemical module    -   y: Electrochemical device    -   Z: Energy system

The invention claimed is:
 1. An electrochemical device comprising atleast one metal material, wherein the metal material is made of a Fe—Crbased alloy that contains Ti in an amount of more than 0.10 mass % and1.0 mass % or less and Cu in an amount of 0.10 mass % or more and 1.0mass % or less.
 2. The electrochemical device according to claim 1,wherein the metal material contains Cr in an amount of 18 mass % or moreand 25 mass % or less.
 3. The electrochemical device according to claim1, wherein the metal material contains no rare earth elements.
 4. Theelectrochemical device according to claim 1, wherein the metal materialis made of a magnetic substance.
 5. The electrochemical device accordingto claim 1, wherein a portion or all of a surface of the metal materialis covered with a metal oxide thin layer.
 6. The electrochemical deviceaccording to claim 1, wherein the metal material is used for at leastone of a separator, a manifold, an interconnector, and a currentcollector.
 7. The electrochemical device according to claim 1,comprising at least an electrochemical element and a reformer, and afuel supply unit which supplies fuel gas containing a reduciblecomponent to the electrochemical element.
 8. The electrochemical deviceaccording to claim 1, comprising at least an electrochemical element andan inverter that extracts electrical power from the electrochemicalelement.
 9. An energy system comprising: the electrochemical deviceaccording to claim 7; and a waste heat management unit that reuses heatdischarged from the electrochemical device.
 10. A solid oxide fuel cellcomprising the electrochemical device according to claim 1, wherein apower generation reaction is caused in the electrochemical device.